Probing Cosmic Strings with Gravitational-Wave Fringe

TL;DR

This paper proposes a method to detect cosmic strings by observing gravitational wave fringes caused by lensing of GWs from binary mergers, enabling probing of small-tension strings beyond current constraints.

Contribution

It introduces a novel gravitational wave fringe detection technique to probe cosmic strings with small tension, independent of specific string models, using high-frequency GW observations.

Findings

Potential to detect cosmic strings with tension below current constraints.

Single GW fringe detection can confirm the presence of a cosmic string.

Method is complementary to light lensing probes.

Abstract

Cosmic strings are important remnants of early-Universe phase transitions. We show that they can be probed by Gravitational Waves (GWs) from compact binary mergers. If such chirping GW passes by a cosmic string, it is gravitationally lensed and left with a characteristic signal of the lensing -- the GW fringe. It is observable naturally through the frequency chirping of GWs. This allows to probe cosmic strings with small tension $\Delta = 8\pi G \mu = 10^{-6} \text{ -- } 10^{-10}$, just below the current constraint, at high-frequency LIGO-band and mid-band detectors. Although its detection rates are estimated to be small, even a single detection can be used to identify a cosmic string. Contrary to the stochastic GW produced from loop decays only in local $U(1)$ models, the GW fringe can directly probe straight strings model independently. This is also complementary to the existing probes with the strong lensing of light.